1. Field of the Invention
This invention relates to an apparatus for accessing any track in a magnetic recording/playback system of the type in which a magnetic recording/playback head is moved radially of a magnetic recording medium (hereafter referred to as a "magnetic disk") on which a number of circular tracks are concentrically arranged to either record a signal on or playback a signal from a predetermined track.
2. Prior Art Statement
Electronic still video camera systems have recently been developed. These systems combine an imaging device such as a solid state imaging element or image pickup tube with a recorder that employs an inexpensive magnetic disk of a comparatively large storage capacity as a storage medium and operate by electronically imaging a subject, recording a still picture of the subject on the magnetic disk and reproducing the recorded picture by a separately provided television system or printer. A still video signal magnetic recording system in which a still picture recorded on a visible recording medium such as ordinary film or photographic paper is imaged and recorded on a magnetic disk, and a still picture playback system in which a still video signal is read from a magnetic disk and reproduced on a television or the like have also been realized.
In conventional still video magnetic recording/playback systems of this kind, the tracks on the recording disk can be accessed only one track at a time. In other words, a conventional system is provided with forward and reverse switches. Pressing the forward switch once feeds a magnetic head one track inward, and pressing the reverse switch shifts the head one track outward. Accordingly, in order to skip several tracks and access a desired track (which is a form of random access), the forward or reverse switch must be pressed a number of times. This is a troublesome operation. In addition, each time the forward or reverse switch is pressed, the system executes control (referred to as "tracking control") so as to position the magnetic head at the center of the next track. Since this takes times, a fairly long access time is required when such tracking control is performed successively for a plurality of tracks. In particular, tracking is very slow in a magnetic recording/playback system because of so-called "peak finding control", according to which the envelope of a read signal is detected while the magnetic head is moved radially of the magnetic disk, and the magnetic head is positioned at a location where the envelope peaks. Thus there is need of a system capable of making high-speed random access feasible.
In all likelihood there are two approaches that can be taken to realize a high-speed random-access system. One would be to create the system from scratch for the purpose of achieving high-speed random access, and the other would be to add the high-speed random-access function to an already existing system by providing the system with some additional circuitry. The latter approach obviously would serve to hold down development costs and shorten development time.